Method and apparatus for transmitting control information in wireless communication systems

ABSTRACT

A method for transmitting control information by a base station in a wireless communication system is provided. The method includes determining a precoder to be applied to a resource and a Demodulation Reference Signal (DMRS) port, the resource being used to transmit the control information, and the DMRS port corresponding to the resource and being used to transmit a DMRS, precoding the resource and the DMRS port by using the determined precoder, and transmitting the control information and the DMRS to a user equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of a U.S.provisional patent application filed on Nov. 16, 2011 in the U.S. Patentand Trademark Office and assigned Ser. No. 61/560,454 and a U.S.provisional patent application filed on Jan. 17, 2012 in the U.S. Patentand Trademark Office and assigned Ser. No. 61/587,351, the entiredisclosure of each of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus fortransmitting control information in wireless communication systems. Moreparticularly, the present invention relates to a method for providing atransmission scheme that allows the transmitted signals to be receivedwith a higher level of diversity order such that reliable transfer ofinformation can be achieved even in mobile channels with dynamicvariations in the time domain and the frequency domain.

2. Description of the Related Art

The present invention relates to a wireless cellular communicationsystem with at least one base station (i.e., an evolved Node B (eNB))and at least one User Equipment (UE). More particularly, the presentinvention relates to a wireless communication system where the eNBschedules both the downlink and uplink transmission to and from the UE.The scheduling is on a per-sub-frame basis and the scheduling indicationis transmitted from the eNB to the UE via the control channel in eachsub-frame of any downlink transmission.

Throughout the present invention, the 3rd Generation Partnership Project(3GPP) Long Term Evolution (LTE) Release 8˜10 is regarded as the legacysystem and the in-development Release 11 and beyond systems are taken asa system where the exemplary embodiments of the present invention can beimplemented. The present invention can also be applied to other cellularsystems where appropriate.

Downlink data information is conveyed through a Physical DL SharedCHannel (PDSCH). Downlink Control Information (DCI) includes DownLinkChannel Status Information (DL CSI) feedback request to UEs, SchedulingAssignments (SAs) for uplink transmission from UEs (UL SAs) or for PDSCHreceptions by UEs (DL SAs). The SAs are conveyed through DCI formatstransmitted in respective Physical DL Control CHannels (PDCCHs). Inaddition to SAs, PDCCHs may convey DCI that is common to all UEs or to agroup of UEs.

In the 3GPP LTE/LTE-Advanced (LTE-A) system, the downlink transmissionemploys Orthogonal Frequency Division Multiple Access (OFDMA) such thatthe entire system bandwidth is divided into multiple subcarriers. Agroup of 12 consecutive subcarriers are referred to as a Resource Block(RB). An RB is the basic unit of resource allocation in the LTE/LTE-Asystem.

FIG. 1 is a diagram illustrating a basic unit of resource allocation inan LTE/LTE-A system according to the related art.

Referring to FIG. 1, in the time domain, the basic unit of resourceallocation in the LTE/LTE-A system is the subframe. Each subframeconsists of 14 consecutive OFDM symbols as shown in FIG. 1. A ResourceElement is the intersection of a subcarrier and an OFDM symbolrepresented by a square in FIG. 1 where a single modulation symbol canbe transmitted.

As shown in FIG. 1, different time and frequency resources can be usedto transmit different signal types. A Cell specific Reference Signal(CRS) is transmitted to support UE mobility, such as initial access,handover operations and to support legacy PDSCH transmission modes. ADemodulation Reference Signal (DMRS) is transmitted to support new PDSCHtransmission modes. Control channels are transmitted to inform the UE ofthe size of the control region, downlink/uplink scheduling assignments,and ACKnowlegement/Non-ACKnowlegement (ACK/NACK) for uplink HybridAutomatic Repeat reQuest (HARQ) operations. A Channel Status InformationReference Signal (CSI-RS) is transmitted to provide UEs with a referencesignal for measuring the downlink channel for CSI feedback purposes. ACSI-RS can be transmitted on any of the group of REs marked with indicesA, . . . , J. Additionally, zero power CSI-RS or muting can beconfigured in which case the RE positions marked by indices A, . . . , Jare not used for the transmission of a reference signal, a data signal,or a control signal. Zero power CSI-RS or muting is used in an LTE-Asystem to enhance the measurement performance of UEs receiving CSI-RSfrom neighboring transmission points. The PDSCH is transmitted in thedata region on REs which are not used for the transmission of CRS, DMRS,CSI-RS, zero power CSI-RS.

As mentioned above, the eNB transmits PDCCH in legacy LTE/LTE-A systemsfor various purposes, such as an uplink/downlink scheduling assignmentor a CSI feedback request indication. Due to the nature of an OFDMAsystem which enhances performance using frequency selective schedulingand simultaneous transmissions to multiple UEs, optimized systemperformance necessitates multiple PDCCHs to be transmitted to multipleUEs. Additionally, supporting Multi-User Multiple Input Multiple Output(MIMO) (MU-MIMO) where PDSCH transmissions for different UEs arespatially separated using antenna technology also requires simultaneousPDCCH transmissions to multiple UEs.

In 3GPP release 8˜10, the control channel is usually transmitted in thebeginning of a sub-frame, so that the UE can efficiently acquire thescheduling information early enough for data decoding. The PDCCH isconfigured to be transmitted in the first one to three OFDM symbols in asub-frame.

In order to provide the system with sufficient capacity for transmittingdownlink/uplink scheduling assignments, a new Control Channel (CCH)named Enhanced Physical Data Control Channel (E-PDCCH or ePDCCH) wasdeveloped in LTE-A Release 11 to cope with the shortage of PDCCHcapacity. A key factor that causes the shortage of PDCCH capacity is thefact that it is transmitted only in the first one to three OFDM symbolsof a subframe. Furthermore, with frequent MU-MIMO transmissions wheremultiple UEs can be scheduled using the same frequency and timeresources, the improvement on LTE/LTE-A systems is severely limited dueto the shortage of PDCCH capacity. Unlike the PDCCH, the ePDCCH istransmitted on the data region of a subframe much like a PDSCH.

PDCCH Structure in LTE Re18

In 3GPP LTE Release 8˜10, a PDCCH is presented in the first several OFDMsymbols. The number of OFDM symbols used for PDCCH is indicated inanother Physical Control Format Indication Channel (PCFICH) in the firstOFDM symbol. Each PDCCH consists of L Control Channel Elements (CCEs),where L=1, 2, 4, 8 representing different CCE aggregation levels, eachCCE consists of 36 sub-carriers distributed throughout the systembandwidth.

PDCCH Transmission and Blind Decoding

Multiple PDCCHs are first attached with a user-specific CyclicRedundancy Check (CRC), independently encoded and rate matched accordingto CCE aggregation level 1, 2, 4 or 8, depending on link qualities, andmultiplexed and mapped to the PDCCH resources. At the UE side, the UEneeds to search for its PDCCHs in a pre-determined search space byassuming a certain CCE aggregation level and using the user-specificCRC. This is called blind decoding as the user may need to try multipledecoding attempts before the PDCCH could be located and identified.

Diversity Achieving Transmission Schemes

In 3GPP LTE Release 8˜10, a PDCCH is transmitted using Space FrequencyBlock Code (SFBC) on multiple eNB transmit antennas. SFBC is a form oftransmission that allows a single modulation symbol from the UE to bereceived at the UE with a diversity order of two. In other words,assuming that the channel from antenna 1 of the eNB to the UE is h1 andthe channel from antenna 2 of the eNB to the UE is h2, SFBC transmissionallows the UE to recover the modulated signal which is scaled by(|h₁|²+|h₂|²). The received modulated signal being scaled by(|h₁|²+|h₂|²) means that the modulated signal has achieved a diversityorder of 2. Without the use of a transmission scheme, such as SFBC, itwould only be possible to achieve a diversity order of 1 in a flatfading channel. Typically, a higher diversity order would mean that thetransmitted signal is more robust against wireless channel variations inthe time or frequency domain. In other words, by achieving a higherdiversity order, the received signal can be recovered with lowerprobability of error compared to the case of a lower diversity order.

SFBC in 3GPP is performed using CRS, which is a common reference signalthat is used with multiple UEs connected to the same cell.

Another method of achieving diversity is by the use of delay CyclicDelay Diversity (CDD). In 3GPP systems, large delay CDD scheme has beendefined as:

$\begin{bmatrix}{y^{(0)}(i)} \\\vdots \\{y^{({P - 1})}(i)}\end{bmatrix} = {{W(i)}{D(i)}{U\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({v - 1})}(i)}\end{bmatrix}}}$

where the precoding matrix W(i) is of size P×v, i=0, 1, . . . , M_(symb)^(ap)−1 is the number of antenna ports, v is the number of transmissionlayer, and M_(symb) ^(ap) is the number of symbols to be precoded by theabove equations. D(i) is a diagonal matrix, and U is a v×v matrix. Thevalue of D(i) and U are predefined matrix dependent on the number oflayers v.

The values of the precoding matrix W(i) are selected among the precoderelements in the codebook configured in the eNB and the UE. For 2 antennaports, the precoder with index zero is selected. For 4 antenna ports,the UE may assume that the eNB cyclically assigns different precoders todifferent vectors [x⁽⁰⁾(i) . . . x^((v-1))(i)]^(T) on the PDSCH. Adifferent precoder is used for every v vector. More particularly, theprecoder selected according to W(i)=C^(k), where k is the precoder indexgiven by

${k = {{\left( {\left\lfloor \frac{i}{v} \right\rfloor {mod}\; 4} \right) + 1} \in \left\{ {1,2,3,4} \right\}}},$

and C₁, C₂, C₃, C₄ denote precoder matrices corresponding to precoderindices 12, 13, 14, 15, respectively, in the four-antenna codebook. Theuse of large delay CDD creates an artificial delay effect on thereceived signal. In an OFDMA system, such delay corresponds to frequencyselectivity and higher order of diversity.

DCI Transmission

A PDCCH transmission refers to a DCI transmission. There can be multipleDCIs targeting for one UE in a subframe, and a DCI could be targetingfor one or multiple UEs. There are multiple types of DCI formats, amongwhich downlink grant carries the resource allocation and transmissionproperties for PDSCH transmission in the present subframe, while uplinkgrant carries the resource allocation and transmission properties forPUSCH transmission in the uplink subframe.

PDSCH Transmission and UE-specific Reference Signals

All those OFDM symbols after the PDCCH region can be assigned as PDSCH.The data symbols are mapped onto the sub-carriers of those OFDM symbolsexcept the resource elements assigned for reference signals.

UE-specific reference signals, i.e., DMRS, are introduced into thesystem for simple implementation for beamforming transmission, wheremultiple antennas are precoded with different weights beforetransmission. In 3GPP LTE Release 8˜10, the UE-specific referencesignals are precoded with the same precoder as that of the datatransmitted in the same resource block. Each resource block consists of14 OFDM symbols in the time domain and 12 subcarriers in the frequencydomain. By applying the same precoding as that applied for the datatransmitted on the same resource block, the UE can estimate the effectof precoding from the UE-specific reference signal without having toreceive some other information which indicates the applied precoding.The UE is thus able to decode the received signals assuming the signalis transmitted from those virtual antenna ports, without knowing theexact precoder information.

FIG. 2 is a diagram illustrating DMRS ports in a resource blockaccording to the related art.

Referring to FIG. 2, the location and port definition of DMRS in 3GPPRelease 10, which can support up to eight ports from #7˜#14 isillustrated. For the case where up to 4 DMRS ports are used, ports#7/8/9/10 are spread with a spreading factor of two in the time domain.For the case where more than 4 DMRS ports are used, all ports are spreadwith a spreading factor of four in the time domain.

There is another subframe structure in the preferred system referred toas a Multimedia Broadcast Single Frequency Network (MBSFN) subframe,where multiple eNBs will transmit identical signaling for broadcastingpurposes. A UE can be configured to receive the MBSFN subframe since notevery UE is the target for MBSFN broadcasting. The system can make useof such a feature to resolve the compatibility as well as high-overheadproblems when new transmission modes are introduced into the system. Forexample in 3GPP, the release-8 UEs will not be able to recognize theDMRS on ports 7˜14 as defined in release 10. The system can configure asubframe as a “MBSFN” subframe to release 8 UEs, while a normal subframewith only DMRS in the PDSCH region is actually transmitted for release10 UEs who can recognize DMRS ports 7˜14 and decode data without CRS.Similar philosophy can also be applied to future evolving systems whennew features are introduced.

However, in a MBSFN subframe where no CRS is defined, the legacy CDDtransmission based on CRS transmission can no longer be configured. Butsuch an open loop MIMO technique is still necessary in some scenarioswhen the feedback is not readily available or reliable, and/or the MIMOchannel is rather selective in frequency and/or time domain.

Therefore, a need exists for a method and an apparatus for transmittingcontrol information in wireless communication systems.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a transmission scheme that allows transmittedsignals to be received with a higher level of diversity order such thatreliable transfer of information can be achieved even in mobile channelswith dynamic variations in the time domain and the frequency domain. Toachieve the aforementioned objectives, the system divides the wirelessresource used for the transmission of a control channel and mapsdifferent antenna ports for each of the divided wireless resourcesegments. A User Equipment (UE) derives the precoding and channelestimation for each wireless resource segment by using a mappingrelationship between multiple wireless resource segments and multipleantenna ports.

In accordance with an aspect of the present invention, a method fortransmitting control information by a base station in a wirelesscommunication system is provided. The method includes determining aprecoder to be applied to a resource and a Demodulation Reference Signal(DMRS) port, the resource being used to transmit the controlinformation, and the DMRS port corresponding to the resource and beingused to transmit a DMRS, precoding the resource and the DMRS port usingthe determined precoder, and transmitting the control information andthe DMRS to a user equipment.

In accordance with another aspect of the present invention, a method forreceiving control information by a user equipment in a wirelesscommunication system is provided. The method includes receiving asubframe from a base station, determining a precoder to be applied to aresource being used to receive the control information by using a DMRS,and demodulating the resource by using the precoder.

In accordance with another aspect of the present invention, a basestation for transmitting control information in a wireless communicationsystem is provided. The base station includes a control unit configuredto determine a precoder to be applied to a resource used to transmit thecontrol information and a DMRS port corresponding to the resource andbeing used to transmit a DMRS, to precode the resource and the DMRS portby using the determined precoder, and to transmit the controlinformation and the DMRS to user equipment.

In accordance with another aspect of the present invention, a userequipment for receiving control information in a wireless communicationsystem is provided. The user equipment includes a control unitconfigured to receive a subframe from a base station, to determine aprecoder to be applied to a resource being used to receive the controlinformation by using a DMRS, and to demodulate the resource by using theprecoder.

Exemplary embodiments of the present invention disclose methods ofenhanced transmission with precoder cycling in the legacy PhysicalDownlink Shared CHannel (PDSCH) region. The proposed schemes can beapplied to both data and enhanced control channel transmission in thelegacy PDSCH region.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a basic unit of resource allocation ina Long Term Evolution (LTE)/LTE-Advanced (LTE-A) system according to therelated art;

FIG. 2 is a diagram illustrating Demodulation Reference Signal (DMRS)ports in a resource block according to the related art;

FIGS. 3A through 3F are diagrams illustrating Resource Element Group(REG) partitioning for transmission of an Enhanced Control CHannel(ECCH) according to exemplary embodiments of the present invention;

FIG. 4 is a diagram illustrating REG partitioning for transmission of anECCH according to an exemplary embodiment of the present invention;

FIGS. 5A through 5C are diagrams illustrating REG-based precodercyclings according to exemplary embodiments of the present invention;

FIGS. 6A and 6B are diagrams illustrating REG-based precoder cyclingsaccording to exemplary embodiments of the present invention;

FIG. 7 is a diagram illustrating precoder cycling among multiple VirtualResource Blocks (VRBs) according to an exemplary embodiment of thepresent invention;

FIG. 8 is a diagram illustrating precoder cycling allocation with apredefined DMRS mapping according to an exemplary embodiment of thepresent invention;

FIG. 9 is a diagram illustrating precoder cycling allocation with apredefined DMRS mapping according to an exemplary embodiment of thepresent invention where a precoding is changed within an REG;

FIG. 10 is a diagram illustrating precoder cycling allocation with apredefined DMRS mapping according to an exemplary embodiment of thepresent invention where a precoding is changed within an REG;

FIG. 11 is a flowchart illustrating a method for transmission of anEnhanced Control CHannel (E-CCH) of an evolved Node B (eNB) according toan exemplary embodiment of the present invention; and

FIG. 12 is a flowchart illustrating a method for reception of an E-CCHof a User Equipment (UE) according to an exemplary embodiment of thepresent invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

In an Orthogonal Frequency Division Multiple Access (OFDMA) basedsystem, the system configures a set of resources for a particular UserEquipment (UE) for either control or data transmission. The set ofresources includes multiple Resource Elements (REs) which can be locatedwithin a Resource Block (RB) or distributed in multiple RBs.Demodulation Reference Signal (DMRS) ports are allocated in the at leastone of multiple RBs for the UE to detect the transmission.

Exemplary embodiments of the present invention are applicable to, butnot limited to, transfer of information on wireless communicationssystems, for example, for use in an Evolved Universal MobileTelecommunications System Terrestrial Radio Access Network.

In exemplary embodiments of the present invention, the multiple REs aregrouped into Resource Element Groups (REGs), where each REG contains atleast one or multiple REs in the frequency and/or the time domain. TheREs for an REG can be consecutive in the frequency and/or the timedomain, or distributed/non-consecutive in the frequency and/or the timedomain.

FIGS. 3A through 12, discussed below, and the various exemplaryembodiments used to describe the principles of the present disclosure inthis patent document are by way of illustration only and should not beconstrued in any way that would limit the scope of the disclosure. Thoseskilled in the art will understand that the principles of the presentdisclosure may be implemented in any suitably arranged communicationssystem. The terms used to describe various embodiments are exemplary. Itshould be understood that these are provided to merely aid theunderstanding of the description, and that their use and definitions inno way limit the scope of the invention. Terms first, second, and thelike are used to differentiate between objects having the sameterminology and are in no way intended to represent a chronologicalorder, unless where explicitly stated otherwise. A set is defined as anon-empty set including at least one element.

FIGS. 3A through 3F are diagrams illustrating REG partitioning fortransmission of an Enhanced Control CHannel (ECCH) according toexemplary embodiments of the present invention.

Referring to FIGS. 3A through 3F, exemplary consecutive REG portioningconfigurations are illustrated. In FIG. 3A, consecutive 2 REs exceptReference Signal (RS) REs in the time domain are grouped as an REG. InFIG. 3B, consecutive 4 REs except RS REs in the time domain are groupedas an REG. In FIG. 3C, consecutive REs except RS REs for the samesubcarrier in the same RB are grouped as an REG. The REG grouping canalso be done in the frequency domain. In FIG. 3D, consecutive 2 REsexcept RS REs in the frequency domain are grouped as an REG. In FIG. 3E,consecutive 4 REs except RS REs in the frequency domain are grouped asan REG. In FIG. 3F, one Orthogonal Frequency Division Multiplexing(OFDM) symbol except RS REs are grouped as one REG. Note for the casesillustrated in FIGS. 3A, 3B, 3D, and 3E, the size of REG (number of REsin an REG) is fixed, while the REG size for the cases in FIGS. 3C and 3Fmay vary from one REG to another based on its actual location. If oneconstrains that an REG needs to be located in one subcarrier for FIGS.3A and 3B, or in one OFDM symbol for FIGS. 3D and 3E, there could beorphan REs which cannot be utilized. Since precoding cycling is going tobe applied RE by RE, it is now necessary for the channel within an REGto be coherent. Thus, an allocation of an REG across subcarriers or OFDMsymbols will improve the efficiency by avoiding the orphan REs. Forexample, in FIG. 3A, REG #4 is allocated in two consecutive OFDMsymbols, and in FIG. 3D, REG #4 is allocated in two consecutivesubcarriers.

FIG. 4 is a diagram illustrating REG partitioning for transmission of anECCH according to an exemplary embodiment of the present invention.

Referring to FIG. 4, 30 REGs are included in one RB. Each REG contains 4REs distributed in the subframe. An REG can also contain multiple REswhich are not consecutive in the frequency and/or the time domain.

The number of REs in an REG can be variable, it can also be one in somecases, i.e., a RE will represent one REG.

Note the indexing in FIGS. 3A through 3F and FIG. 4 is done within an RBeither in frequency or time domain. When multiple RBs are allocated forthe transmission with precoder cycling, the indexing can be also donethrough the multiple RBs either in frequency or time domain.

Multiple REGs maybe further be grouped into another resource set,namely, an Enhanced Control Channel Element (E-CCE), which will be theunit for enhanced control channel transmission. An E-CCE may containmultiple REGs across multiple RBs, or one or multiple REGs within oneRB. An Enhanced-Physical Downlink Control CHannel (E-PDCCH) will betransmitted using at least one E-CCE or multiple E-CCEs. In anotherapplicable transmission, the schemes in exemplary embodiments of thepresent invention can also be applied to other enhanced controlchannels, such as an Enhanced Physical HARQ Indication Channel(E-PHICH), or an Enhanced Physical Control Format Indication Channel(E-PCFICH).

Exemplary Embodiment 1 REG Based Precoding Cycling

A unified precoding definition can be defined similar to the large delayCyclic Delay Diversity (CDD) in legacy systems:

$\begin{bmatrix}{y^{(7)}(i)} \\\vdots \\{y^{({6 + v})}(i)}\end{bmatrix} = {{W(i)}{D(i)}{{U\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({v - 1})}(i)}\end{bmatrix}}.}}$

For non-CDD transmission, one can define D(i)=U=I_(v), where I_(v) isthe identity matrix, so that the precoding is simplified to:

$\begin{bmatrix}{y^{(7)}(i)} \\\vdots \\{y^{({6 + v})}(i)}\end{bmatrix} = {{{W(i)}\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({v - 1})}(i)}\end{bmatrix}}.}$

Note that exemplary embodiments of the present invention can be appliedwith both the CDD and non-CDD precoding as defined above. An exemplaryembodiment of the present invention discloses methods of how W(i) isdetermined for each symbol.

In an exemplary embodiment of the present invention, the system assignsa set of REGs for control or data transmission for a particular UE. Theresource allocation of the set of REGs can be previously indicated tothe UE, or the UE may identify the allocation by blind decoding alimited number of possible resource combinations.

Assume N REGs are assigned to the UE, with respective size l_(REG) ^(n)for each REG n. Define i′ as the REG index where the i-th symbol islocated. Note that i′ is deduced depending on the REG configurations.For example, in a frequency domain partitioning as illustrated in FIGS.3D, 3E, and 3F,

$i^{\prime} = {\arg \underset{i^{''}}{\; \max}{\left( {i > {\sum\limits_{n = 0}^{i^{''}}l_{REG}^{n}}} \right).}}$

More particularly, the precoder is selected according toW(i)=W′(i′)=C_(k), where k is the precoder index given by

${k = {{\left( {\left\lfloor \frac{i^{\prime}}{v} \right\rfloor {mod}\; M} \right) + 1} \in \left\{ {1,2,\ldots \mspace{14mu},M} \right\}}},$

and C₁, C₂, . . . , C_(M) denote a subset of precoder matrices in thecodebook corresponding to the number of transmit antennas. If thetransmission rank is restricted to one, the precoding selection can besimplified to k=(i′ modM)+1∈{1, 2, . . . , M}, which is dependent on theREG index.

In an exemplary embodiment of the present invention, the UE will deducethe precoding information for each of its allocated REGs by the rulesspecified above regardless of whether the allocated REGs are localizedor distributed.

FIGS. 5A through 5C are diagrams illustrating REG-based precodercyclings according to exemplary embodiments of the present invention.

Referring to FIGS. 5A through 5C, multiple UEs are multiplexed withinone Primary Resource Block (PRB) using the same antenna ports 7-10. Theprecoding matrix W(i) is applied to the DMRS port 7-10. W(i) isdetermined by the REG index within each UE's allocation.

FIGS. 6A and 6B are diagrams illustrating REG-based precoder cyclingsaccording to exemplary embodiments of the present invention.

Referring to FIGS. 6A and 6B, the precoding can be cycling inside anREG. FIGS. 6A and 6B illustrate an example of when an REG is asubcarrier within an RB. i″ is defined as the RE index for symbol iwhich is located within REG i′. The precoder is selected according toW(i)=W′(i′)=C_(k), where k is the precoder index given by

${k = {{\left( {\left\lfloor \frac{i^{''}}{v} \right\rfloor {mod}\; M} \right) + 1} \in \left\{ {1,2,\ldots \mspace{14mu},M} \right\}}},$

and C₁, C₂, . . . , C_(M) denote a subset of precoder matrices in thecodebook corresponding to the number of transmit antennas. If thetransmission rank is restricted to one, the precoding selection can besimplified to k=(i″ modM)+1∈{1, 2, . . . , M}, which is dependent on theREG index.

It can be extended to other exemplary embodiments of the presentinvention that W(i) is dependent on the global REG index within theallocated Virtual Resource Block (VRB) for the special transmission,e.g., for an enhanced control channel transmission, or dependent on therelative REG index within an RB.

When a UE is allocated with multiple REGs which are distributed inmultiple RBs, the same precoder definitions can be applied to each RB.Alternatively, the precoder can have a further cycling on an RB index ora subframe index. For example, the k=((i′+F)modM)+1∈{1, 2, . . . , M},where F=F(n_(RB), n_(subframe)) is a predefined function depending onthe RB index n^(RB) where the REG is located, and/or the subframe indexn_(subframe) where the REG is located. For example, F=F(n_(RB),n_(subframe))=n_(RB)·n_(subframe).

For intra-REG precoder cycling case, the precoder can have a further REGindex, and/or cycling on an RB index, and/or a subframe index. Forexample, the k=((i″+F) modM)+1∈{1, 2, . . . , M}, where F=F(i′, n_(RB),n_(subframe)). FIG. 6B illustrates an example for the case where M=4 andF=i′.

In an exemplary embodiment of the present invention, the precoder setC₁, C₂, . . . , C_(M) can change from RB to RB. For example, assumingthere are N VRBs allocated for E-PDCCH precoder cycling transmission,the symbols in the n-th VRB will use a precoder subset C₁ ^((n)), C₂^((n)), . . . , C_(M) ^((n)). For example, the REs in VRB 1 will cyclebetween P₁, P₂, the REs in VRB 2 will cycle between P3, P₄, and so on.Here, {P_(i)} is the full set or a subset of the precoders in thecodebook.

In an exemplary embodiment of the present invention, for the n-th VRB,only one precoder C₁ ^((n)) is defined, and the precoder changes fromone VRB to another. Inside the VRB, all UEs scheduled will use the sameprecoder for demodulation, as illustrated in FIG. 7.

FIG. 7 is a diagram illustrating precoder cycling among multiple VRBsaccording to an exemplary embodiment of the present invention.

Referring to FIG. 7, it is assumed that the control/data payload toresource mapping follows the same order of REG resource allocation,i.e., if the REG is allocated in time domain as in FIGS. 3A, 3B, or 3C,the payload symbols will also be mapped to REs in the time domain first.In a 3GPP system, the legacy RE mapping follows the frequency firstrule. When the frequency first rule is applied, the determination of i′and i″ for payload symbol i will become more complex, but the sameprecoder mapping as described above will still apply. It should also benoted that REG interleaving is done before actual resource mapping ofdata symbols to physical REs, the REG interleaving may use the sameinterleaver used for legacy PDCCH REG interleaving as defined in 3GPPrelease 8˜10.

Spreading or repetition can also be done across multiple REs in additionto the precoder cycling. For example, a control data symbol istransmitted on 4 neighboring REs with a spreading code of factor 4, andall those 4 REs use the same precoder. In a case of repetition, e.g., acontrol data symbol is repeatedly transmitted on 4 neighboring REs, eachRE can use a different precoder. The neighboring REs can be a predefinedREG. Such schemes of precoder cycling with spreading or repetition maybe used for E-PHICH or E-PCFICH transmission in practice. E-PHICH isused for the indication of ACK or NACK by an eNB in response to theuplink transmissions made by a UE. E-PCFICH is used for the indicationof the control region size that is used for the transmission of PDCCH orE-PDCCH. For PDCCH, E-PCFICH would indicate the number of OFDM symbolsused for the transmission of PDCCH while for the E-PDCCH, E-PCFICH wouldindicate the number of RBs used for the transmission of E-PDCCH.

In summary, an exemplary method is disclosed so that:

-   -   The REs in an RB are partitioned into one or several subsets,    -   Each subset of REs in an RB is precoded using a predefined        precoder,    -   The precoder set applied for each RB may or may not change from        RB to RB,    -   The REs in one of the RE subset may be allocated for different        UEs, and    -   A UE utilizes the reference signal inside the RB for channel        estimation, and demodulates data symbols together with the        predefined precoder set information.

Exemplary Embodiment 2 REG and DMRS Port Cycling

In the previously described exemplary embodiment 1, W(i) is decidedbased on the REG location/index. It should be assumed that the UE knowsthe exact W(i) being applied for each REG.

In an exemplary embodiment of the present invention, the UE can decodethe transmission by using precoded DMRS without knowledge of which W(i)is used for each REG. The UE should assume the precoding for spatialmultiplexing using antenna ports with UE-specific reference signals inthe legacy system, which is defined as:

$\begin{bmatrix}{y^{(7)}(i)} \\\vdots \\{y^{({6 + v})}(i)}\end{bmatrix} = {\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({v - 1})}(i)}\end{bmatrix}.}$

For each REG, the UE should assume it is transmitted using a specificDMRS. Rules should be designed so that the UE knows the DMRS portconfiguration for each REG.

FIG. 8 is a diagram illustrating precoder cycling allocation with apredefined DMRS mapping according to an exemplary embodiment of thepresent invention.

Referring to FIG. 8, precoding allocation with predefined DMRS mapping,where REG i′ is transmitted using DMRS port 7+(i′ modM), where M=4 isillustrated. For each allocated REG, the UE will use corresponding DMRSports for demodulation. Similar to the exemplary embodiment 1 of thepresent invention, the REG index here can be defined within an RB, orwithin a set of pre-allocated RBs.

The actual precoder applied to each REG in FIG. 8 is transparent to theUE. The eNB can choose to rotate using the entire codebook, a subset ofthe codebook, or any other precoder the eNB finds appropriate.

When a UE is allocated with multiple REGs which are distributed inmultiple RBs, the same REG and DMRS port mapping can be applied to eachRB. Alternatively, the precoder can have a further cycling on an RBindex or a subframe index. For example, REG i is transmitted using DMRSport 7+[(i+F)modM], where F=F(n_(RB), n_(subframe)) is a predefinedfunction depending on the RB index n_(RB) where the REG is located,and/or the subframe index n_(subframe) where the REG is located. Forexample, F=F(n_(RB), n_(subframe))=n_(RB)·n_(subframe).

Intra-REG cycling is also possible for this DMRS port based precodingcycling. An example is illustrated in FIG. 9, where the UE assumes DMRSports 7-10 for decoding of one of the four REs in an REG. The intramapping rule can be defined as the RE i″ in REG i′ is transmitted usingDMRS port 7+[(i″+F)modM], where F=F(i′, n_(RB), n_(subframe)). FIG. 9illustrates an example for the case where M=4 and F=i′.

FIG. 9 is a diagram illustrating precoder cycling allocation with apredefined DMRS mapping according to an exemplary embodiment of thepresent invention where a precoding is changed within an REG.

Referring to FIG. 9, precoder cycling is done using four precoders W0,W1, W2, W3 with DMRS port 7, port 8, port 9, and port 10. The eNB mayalso change the precoder used for each DMRS port from RB to RB, e.g.,port 7/8 uses W1/W2 in VRB 1, and uses W3/W4 in VRB 2, and so on. Thisoperation is transparent to the UE, as the UE only utilizes the DMRSinside each RB for demodulation.

In an exemplary embodiment of the present invention, the system may onlyconfigure one DMRS port for an RB, e.g., all the REs use port 7 fordemodulation assuming rank-1 transmission. The eNB may change precoderfrom VRB to VRB, which is transparent to the UE. In this case, as onlyone-port DMRS is transmitted, the DMRS power for port 7 can be boostedwith 3dB as no port-8 DMRS is transmitted. The configuration is similarto that in FIG. 6, except that only DMRS port 7 isconfigured/transmitted in the allocated REs.

FIG. 10 is a diagram illustrating precoder cycling allocation with apredefined DMRS mapping according to an exemplary embodiment of thepresent invention where a precoding is changed within an REG.

Referring to FIG. 10, REG allocation where the REs in an REG are groupedin a hybrid manner is illustrated. In FIG. 10, precoder cycling is doneusing two precoders W0 and W1 with DMRS port 7 and port 8. In a firstgroup of OFDM symbols, e.g., 2 (if no PDCCH is configured), 3, 4, 7, 8,11, an REG consists of two REs across the frequency domain, while in asecond group of OFDM symbols, e.g., 5, 6, 9, 10, 12, 13, an REG consistsof two REs across the time domain. In the first group of OFDM symbols,there could be CRS, and/or an Enhanced Control CHannel (E-CCH), and/orPDSCH scheduled, in the second group of OFDM symbols, there could beDMRS, and/or CSI-RS, and/or E-CCH, and/or PDSCH scheduled. Note thatsuch a grouping can be applied to both transmit diversity and precodercycling modes. For transmit diversity, space-frequency block code isapplied to the first group of OFDM symbols, whiles space-time block codeis applied to the second group of OFDM symbols. For precoder cycling,two different precoders can be applied to the two REs in an REG, asillustrated in FIG. 9. In summary, the OFDM symbols inside an RB pair ora subframe are categorized into at least two types, for the first typeof OFDM symbols, the REs are grouped along the frequency domain. For thesecond type of OFDM symbol, the REs are grouped along the time domainacross two contiguous OFDM symbols of the second type. For example in anormal subframe of 3GPP system, the OFDM symbols of the first typeinclude symbols #0, #1, #2, #3, #4, #7, #8, #11, the OFDM symbols of thesecond type include symbols #5, #6, #9, #10, #12, #13, assuming the 14symbols inside one normal subframe are indexed from 0 to 13.

Note that in all the resource allocation as illustrated in FIGS. 4through 10, the REG indexing is for illustration purpose and subjectedto further interleaving before actual assignment to multiple UEs.

Spreading or repetition can also be done across multiple REs in additionto the port cycling. For example, a control data symbol is transmittedon 4 neighboring REs with spreading code of factor 4, and all 4 REs usethe same port. In a case of repetition, e.g., a control data symbol isrepeatedly transmitted on 4 neighboring REs, and each RE can use adifferent port. The neighboring REs can be a predefined REG. Suchschemes of port cycling with spreading or repetition may be used forE-PHICH or E-PCFICH transmission in practice.

In summary, another exemplary method is disclosed so that:

-   -   The REs in an RB are partitioned into one or several subsets,    -   Each subset of REs in an RB is mapped to a predefined DMRS port,    -   The precoder applied for each DMRS port may or may not change        from RB to RB,    -   The REs in one of the RE subset may be allocated for different        UEs, and    -   A UE utilizes the reference signal inside the RB for channel        estimation of each DMRS port, and demodulates each data symbol        with the predefined DMRS port channel.

FIG. 11 is a flowchart illustrating a method for transmission of anE-CCH of an eNB according to an exemplary embodiment of the presentinvention.

Referring to FIG. 11, the eNB first configures the E-CCH region andcorresponding DMRS information, such as the number of ports configuredand a scrambling sequence used for those UEs that will receive the E-CCHat step 1110. Thereafter, the eNB schedules a number of UEs for eachsubframe at step 1120. If a UE is configured using E-CCH, the eNB willcontinue to schedule the E-CCH for the UE. Thereafter, the eNB decideson the precoding to be used for the scheduled UE according to thepredefined rules at step 1130. The possible rules are described in theexemplary embodiments of the present invention. Thereafter, the eNBtransmits the E-CCH to the UE at 1140.

FIG. 12 is a flowchart illustrating a method for reception of an E-CCHof a UE according to an exemplary embodiment of the present invention.

Referring to FIG. 12, the UE first receives the configuration from theeNB on the E-CCH region and corresponding DMRS information, such as thenumber of ports configured and a scrambling sequence used at step 1210.Thereafter, the UE continues to receive the transmitted subframe fromthe eNB at step 1220. Thereafter, the UE generates search spaces foreach possible E-CCH resource combination at step 1230. For each searchspace, the UE decides the corresponding number of DMRS ports for eachREG/RE of the search space according to the rules described in theexemplary embodiment 2 at step 1240.

The UE performs channel estimation for each configured DMRS port, anduses the estimated DMRS channel for corresponding REG/RE demodulation atstep 1250. Thereafter, the UE will go through the search space for E-CCHblind decoding.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting control information bya base station in a wireless communication system, the methodcomprising: determining a precoder to be applied to a resource and aDemodulation Reference Signal (DMRS) port, the resource being used totransmit the control information, and the DMRS port corresponding to theresource and being used to transmit a DMRS; precoding the resource andthe DMRS port using the determined precoder; and transmitting thecontrol information and the DMRS to a user equipment.
 2. The method ofclaim 1, wherein the resource and the DMRS port corresponding to theresource are predefined.
 3. The method of claim 1, further comprising:configuring a control information transmission region and a DMRS portnumber.
 4. The method of claim 1, wherein the resource includes at leastone of a Resource Element (RE), a Resource Element Group (REG), and aResource Block (RB).
 5. A method for receiving control information by auser equipment in a wireless communication system, the methodcomprising: receiving a subframe from a base station; determining aprecoder to be applied to a resource being used to receive the controlinformation by using a Demodulation Reference Signal (DMRS); anddemodulating the resource by using the precoder.
 6. The method of claim5, wherein the resource and a DMRS port corresponding to the resourceare predefined.
 7. The method of claim 5, further comprising: receivinga configuration of a control information transmission region and of aDMRS port number.
 8. The method of claim 5, wherein the resourceincludes at least one of a Resource Element (RE), a Resource ElementGroup (REG), and a Resource Block (RB).
 9. A base station fortransmitting control information in a wireless communication system, thebase station comprising: a control unit configured to determine aprecoder to be applied to a resource used to transmit the controlinformation and a Demodulation Reference Signal (DMRS) portcorresponding to the resource and being used to transmit a DMRS, toprecode the resource and the DMRS port by using the determined precoder,and to transmit the control information and the DMRS to user equipment.10. The base station of claim 9, wherein the resource and the DMRS portcorresponding to the resource are predefined.
 11. The base station ofclaim 9, wherein the control unit is further configured to configure acontrol information transmission region and a DMRS port number.
 12. Thebase station of claim 9, wherein the resource includes at least one of aResource Element (RE), a Resource Element Group (REG), and a ResourceBlock (RB).
 13. A user equipment for receiving control information in awireless communication system, the user equipment comprising: a controlunit configured to receive a subframe from a base station, to determinea precoder to be applied to a resource being used to receive the controlinformation by using a Demodulation Reference Signal (DMRS), and todemodulate the resource by using the precoder.
 14. The user equipment ofclaim 13, wherein the resource and a DMRS port corresponding to theresource are predefined.
 15. The user equipment of claim 13, wherein thecontrol unit is further configured to receive a configuration of acontrol information transmission region and of a DMRS port number. 16.The user equipment of claim 13, wherein the resource includes at leastone of a Resource Element (RE), a Resource Element Group (REG), and aResource Block (RB).